1. Field of the Invention
The present invention relates to an oil pump in which pulsation vibration due to dynamic pressure on the discharge port side can be attenuated.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2005-146998 discloses an oil pump comprising a torocoid-toothed or similar rotor for attenuating the vibration and so on due to pulsation on the discharge port side thereof. Japanese Patent Application Laid-open No. 2005-146998 discloses the provision in a part of the discharge port of a throttle of reduced cross-sectional area. The application also discloses the provision in the vicinity of the discharge port in the downstream side thereof of an oil chamber that communicates with the discharge port by way of the throttle.
The oil chamber communicates with the discharge port by way of a narrow communication hole that communicates in the vertical direction with a flow channel of the discharge port, is formed in a rectangular shape extending in parallel with a linear section of the flow channel of the discharge port, and is arranged sidelong in parallel with the discharge port. In this way, Japanese Patent Application Laid-open No. 2005-146998 discloses an oil chamber of a configuration in which a narrow communication hole is provided in the vertical direction with the discharge port to afford communication therewith.
As is disclosed in Japanese Patent Application Laid-open No. 2005-146998, the oil chamber is provided in parallel and in a juxtaposed state with a linear flow channel of the discharge port. A communication hole (oil inflow port) by which the oil chamber communicates with the discharge port is formed in a vertical direction with respect to the linear flow channel of the discharge port. Accordingly, the communication hole is provided sideways at right angles to the flow direction of the oil in the flow channel of the discharge port.
The oil pump implements a pump operation in which oils is suctioned through an intake port and propelled out through a discharge port as the volume of a plurality of pump chambers within a casing thereof is continuously caused to fluctuate. As a result, pressure is generated in the oil that flows to the discharge port and a pulsing of the oil being propelled out occurs resulting in changes in the amplitude (pulsation) of the discharge pressure.
The pulsation of the oil in the discharge port is produced by pressure in the flow direction of the oil (dynamic pressure) and pressure in all directions in the discharge port (static pressure). The dynamic pressure, which constitutes the main cause of the pulsation, creates load on the devices and pipe members and so on through which oil from the oil pump is supplied and, in addition, as a result of the resonance thereof, leads to increased noise.
Absorption of pulsation due to dynamic pressure in the discharge port is hard to achieve in the oil chamber of Japanese Patent Application Laid-open No. 2005-146998 described above because direct introduction of the dynamic pressure in the flow direction of the oil into the oil chamber is difficult. The reason for this is because the oil chamber is provided sideways and in a juxtaposed arrangement with the discharge port, and the communication hole that affords communication between the discharge port and the oil chamber is provided at right angles to the flow direction of the oil of the flow channel of the discharge port.
Reduction of the static pressure pertaining to the pulsation of oil in the discharge port is possible by introduction by way of the communication hole of the dynamic pressure to the oil chamber provided in the lateral direction (side direction) of the flow channel of the discharge port. However, as the dynamic pressure is generated along the flow direction of the oil and the introduction thereof into the oil chamber in a direction other than the flow direction is difficult, in reality an essentially negligible reduction is achieved.
Accordingly, absorption of the dynamic pressure of pulsation is difficult in an oil chamber that communicates at right angles with respect to the flow direction of the oil in the flow channel of the discharge port and, as a result, achieving an adequate pulsation reduction is difficult.
Consequently, in conventional oil chambers an adequate effect in terms of reducing the pulsation due to dynamic pressure cannot be achieved, and reduction of the unwanted effects on other devices, and reduction of noise and so on, is difficult.